1. Field of the Invention
The present invention relates to a combination weighing and counting apparatus and, more particularly, to a drive apparatus for at least one vibrating feeder used in the combination weighing and counting apparatus.
2. Description of the Prior Art
A combination weighing and counting apparatus utilizing vibrating feeders is shown in a schematic side sectional representation in FIG. 1. The illustrated combination weighing and counting apparatus is supported on a machine base frame BF, and articles M transported by means of a supply conveyor 22 are supplied onto a center portion of a dispensing feeder 25 of a vibrating type through a supply chute 24. A number N of vibrating feeders 1 (1-1 to 1-n) are radially disposed around and in the vicinity of an outer periphery of the dispensing feeder 25 and are so mounted on a frame F, which is in turn supported by the machine base frame BF, as to receive articles M dispensed radially outwardly from the dispensing feeder 25 while the latter is vibrated. The vibrating feeders 1 when vibrated at a predetermined amplitude and a predetermined frequency cause the articles M, received thereby, to move radially outwardly and then fall downwardly onto corresponding pool hoppers 26 (26-1 to 26-n) that are arranged in a circular row on the frame F at respective locations immediately below radially outer ends of the vibrating feeders 1.
The articles M transported by means of the vibrating feeders 1 are, after having been temporarily pooled in the pool hoppers 26 (26-1 to 26-n) and after discharge gates 27 (27-1 to 27-n) of some of the pool hoppers 26 (26-1 to 26-n) that have been selected according to a weighing operation has been subsequently opened, supplied onto weighing hoppers 28 (28-1 to 28-n) that are also mounted on the frame F at respective locations immediately below and in alignment with the pool hoppers 26 (26-1 to 26-n). The weight of the articles M within each of the weighing hoppers 28 is measured by a corresponding weight detecting means 30 (30-1 to 30-n) such as a load cell from which a weight detection signal can be outputted. Based on this weight detection signal, a combination calculation is performed by a combination selecting means 20 built in a control device 31, and some of the weighing hoppers 28 which result in the total weight of the articles M in those weighing hoppers 28 that falls within a tolerance range determined based on a target weight are selected, followed by opening of respective discharge gate 29 (29-1 to 29-n) of the selected weighing hoppers 28 with the articles M consequently collected onto associated collecting chutes 32. The articles M so collected in the collecting chutes 32 are then discharged through a timing hopper 33. The articles M discharged from the timing hopper 33 are packaged by a bagging machine 34 in a bag containing the articles M of a total weight equal to or substantially equal to the target weight.
The weighing hoppers 28 that have been emptied as a result of the previously described weighing operation perform the subsequent cycle of weighing operation after the articles have been supplied from the pool hoppers 26 during the subsequent weighing subsequent, and the vibrating feeders 1 that have supplied the articles onto the emptied pool hoppers 26 are simultaneously driven. After a predetermined quantity of articles have been supplied onto the pool hoppers 26, the associated vibrating feeders 1 terminate their delivery operation and are held at a stand-by state. The foregoing operation of the combination weighing apparatus is executed under the control of the control device 31.
Each of the vibrating feeders 1 comprises a vibrating mechanism including an electromagnet powered by an alternating current source, a movable body and leaf springs, and a trough adapted to be vibrated by the vibrating mechanism, wherein the length of time during which an electric power is supplied from the alternating current source to the electromagnet through a switching element comprised of a solid state relay (SSR) is adjusted by controlling the firing angle of the switching element and the articles on the trough are transported by vibrating the trough somewhat diagonally upwardly by the effect of a magnetic force of attraction, developed by the electromagnet, and a force of restoration developed by the leaf springs that are released from the magnetic force of attraction.
As hereinabove discussed, the plural vibrating feeders 1 are disposed radially around the dispensing feeder 25 and are so constructed that some of the vibrating feeders 1 associated with the plural emptied pool hoppers 26 can simultaneously perform transport operations. Since the prior art method of driving the vibrating feeders 1 is such that the plural vibrating feeders 1 can be driven simultaneously and in phase synchronized fashion to each other, the frame F to which the vibrating feeders 1 are mounted undergoes a considerable vibration in a vertical direction, that is, up and down vibration. This up and down vibration of the frame F adversely affects the weight detecting means that is also mounted on the same frame F, resulting in reduction of the weighing accuracy.